


Brother in Law

by LazyAf



Series: Where Harry potter met each and every persona of muzan kibutsuji [1]
Category: Harry Potter - J. K. Rowling, 鬼滅の刃 | Kimetsu no Yaiba (Manga)
Genre: Akaza just wanted to report, Badass Harry Potter, Crack, Crack Crossover, Crack Treated Seriously, Immortal Harry Potter, M/M, Master of Death Harry Potter, The Author Regrets Nothing, Uncle Harry
Language: English
Status: In-Progress
Published: 2020-11-10
Updated: 2020-11-10
Packaged: 2021-03-09 04:55:13
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,022
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27489178
Author URL: https://archiveofourown.org/users/LazyAf/pseuds/LazyAf
Summary: Muzan's first meeting with his brother in law was something that shall not be spoken to anyone, Ever. Any demon who dares to even form such word will be dealt with a long, torturous death and he made sure that the warning was delivered successfully with the horrified Upper moon who was unfortunate enough to be there to report his useless narration of their futile search for the Blue spider lily.
Relationships: Muzan Kibutsuji/Harry Potter
Series: Where Harry potter met each and every persona of muzan kibutsuji [1]
Series URL: https://archiveofourown.org/series/2008807
Comments: 12
Kudos: 66





	Brother in Law

**Author's Note:**

> Fight me.  
> Where Harry potter met each and every persona of muzan kibutsuji- Every series is different from the each one. They don't connect at each other.

Muzan's first meeting with his brother in law was something that shall not be spoken to anyone, Ever. Any demon who dares to even form such word will be dealt with a long, torturous death and he made sure that the warning was delivered successfully with the horrified Upper moon who was unfortunate enough to be there to report his useless narration of their futile search for the Blue spider lily.

Akaza still has his worth after all. It would be a hassle to find a demon strong enough to take the pinknette's place and have the word spread out that the unchanging position of the upper moon has been broken after centuries.

He didn't even know that Rei has any kind of relation to that kind of person. Only choosing them as his recent pretend family due to the woman having high connection to her to a pharmaceutical company and to blend into the human society.

3 weeks after the planned meeting, Rei Shirota became Tsukihiko Yamada’s Wife. A recent widower whose husband died to an unknown cause which was surprisingly not his doing, leaving the wife, her 5 years old child and a company behind.

The woman was immediately besotted by his charm and obvious wealth and it didn't take long before she agreed to marry him. The daughter, a child that didn't grate his sensitive hearing that much nor an overly curious one to question who Muzan was and what he does, was acceptable.

Rei and Yuri seems too attached to their estate to move out. too many cherished memories, the doe eyed woman explains while gazing at the place with fond eyes. It works for the demon king since that means he didn't have to provide one of his mansions for his 'new' family.

He too, is curious at the estate when he first stepped into the gate and felt a welcoming sense of feeling coming from it, probing him with cautious waves at first before seemingly accepting him in the house. It almost made him feel on edge but he brushed it off, if anyone dares to attack him, he could always deal with the threat without having to lift a finger.

The hallways were filled with paintings which look far too real and lifelike. Frozen in moments of time that even made Muzan, who travelled and seen the wonders of the ever-advancing world, to stop dead in his tracks to admire a painting of a castle surrounded by a dark ethereal lake. And if he looks closely, with little worry about his grace, could see the details of magical creatures hiding underneath and the dark forest behind.

'Hogwarts' it says.

What a dreadful title.

He wonders why he hasn't heard of the painter. Works like these bounds to carry recognitions throughout the world. He could ask Rei where she got them from, maybe even commission the artist at some point.

(and possibly turn them too so They'll paint for Muzan forever.)

There's a lot of places left undiscovered even after weeks of living in the estate. He could blame it on his work to find the cure and family bonding time that Rei always insist upon- which he couldn't always refuse since it will make him suspicious to prying eyes.

Muzan doesn't think that shopping is a bonding time for a man like him. His servants knew to stay away when he's near unless they want to face his wrath so he doesn't have to worry about them walking upon their lord carrying a child in his arms.

A month into his marriage, Muzan encountered...

_him_.

The Demon king and the Upper moon has been lounging in the living room of his dear 'wife' while said woman and child has been away for another shopping trip in the district. The chair is comfortable and the room gives off a strange warmth that seep in his cold body like a blanket in the midst of winter.

A perfect place for a being like him to listen to another useless report of his 'Subordinates' kneeling a good distance away from him while sipping on a rather strong brand of alcohol that pleasantly burns through his throat.

His ‘family’ will be back soon from their extravagant shopping trip and Muzan will enjoy his alone time in this warm place before pretending to be a loving, doting husband and father once again. Akaza only dropped by to apologize for his displeasing his sire at another unsuccessful search for the Blue spider lily.

Since Akaza slaughtered a slayer rumored to become a Hashira in a few months, Muzan let it be. He didn’t want to disrupt good mood just because of his Moon’s incompetency to search for their only purpose and was about to dismiss him.

That was when the fireplace burst into green. From what he heard, Fireplaces doesn't burst into green flames like that- and a man stepped out of it, patting his sleeve to remove any dirt while humming a tune under his breath. The intruder didn't notice them at first, removing his robe and dropping it on the floor and the two could only stare with bewilderment at the man that stepped out of the fireplace like its the most normal thing in the world

The man stop short as soon as his spectacled eyes connects to his plum red ones.

There's a completely stunned silence. One, because no person jump out of a fireplace like some magic-man. Two, They didn't expect someone to walk into them and not sense his arrival from afar. Three...

They never really got to think about number three.

A blink.

A flash of light and Akaza, preciously intent on silencing the man for having the unfortunate timing of stumbling upon a important meeting and a possible jeopardy of Muzan's human life by snitching on his recent wife, crumpled in front of the figure.

And he's not the only one.

The warm feeling that saturated air around him suddenly grew malicious and constrict his body like a snake. A sensation of pinpricks spreads all over his body, a sensation he never felt in a long time, a warning in the air that dared Muzan to do anything that will cost his head to fly out of his shoulder. The surprised grunt from the upper moon three told him he’s not the only one to feel the sudden change in the air.

Muzan soon finds himself immobile, frozen in the chair as if every muscles, tentacles or barbs in his body suddenly refused to cooperate. He has half a mind to command Nakime to get him out of here but that will just make this person see him as a coward. And a Coward Muzan will never be.

His hands shook, eyes desperately moving to catch the approaching figure of the intruder of his and nothing more, much to his rising anger.

It was humiliating. Pure and simple. To think that the most powerful demon of all kind, feared by both his enemies and servants alike, was rendered incapable under the eyes of this... Human like he's filth. It didn't help that Akaza was on the floor struggling like a worm.

Muzan hated whatever power holding him in place but as much as he hated to admit it, its pretty damn useful to restrict an insignificant worm in place. He has a similar ability among his many by controlling his cells flowing inside the demon to do what he willed them to, but in the possession of a mere human?

The attacker was surely not a demon, nobody could be dumb enough to humiliate the Progenitor of demons and get away with. The day that that will happen will be the day that Muzan will have a pleasant evening with the current Ubuyashiki head laughing merrily while skipping in the rain. It wasn’t one those damn Slayers too, the lack of wisteria or distinctive smell of nichirin blade that they like to wave around and slain his kind, present.

It’s just a mysterious man appearing out of nowhere in his current resting place. (Doesn’t that make the man intruder? ) His instinct screams at him that this man is different unlike any being he encountered in his life. There’s just an air around him that reminds the Progenitor of demons of his days as a sickly and dying human fated to die before he can even reach his 20’s

What is he?

A Shaman? A monk who secretly placed hidden talisman in place around the house to trap him? Muzan has his fair share of amusing encounters with such people back in the days, more spiritual and seemed to be blessed by their ‘gods’ to battle ‘evil beings’ like him. He never fails to put them in their place and even watch in amusement when they abandon their beliefs as soon as they became a demon and slaughtered the people they always preached to protect.

But this man.

He’s something _more_.

What, he doesn’t know yet and it infuriates him to no end, nobody dares to go against him except those foolish slayers and nobody survives his ire. This man is no exception even with that interesting abilities of his, It’s best to get rid of the problem before it flourished before his eyes.

He could only glare at the place his useless demon was with his motionless head, the last thing he managed to move before that flash of light, listening with rapt attention as the unknown man slowly moved in his direction with purposeful steps that swayed with his European clothing in the dark.

Muzan glowered at the offending piece of clothing that stopped just a few feet away from him. Nobody was able to make him this helpless, not since _that_ man all those centuries ago and it made him tremble in rage. Once he gets out of this blasted chair, he will cherish every cries of pain as he tears the arrogant man’s skin into pieces, maybe even turn him into a demon just so he can do it again and again without the man dying unless he says so. 

There's a sound of metal being unsheathe and a sword was suddenly pointed in his face. The point of the metal rested on his chin, He could smell the poisonous venom of a snake coating the base and- and his head was slowly lifted to meet the man's eyes. Through the semi-dark room lightened only by the fireplace, the man's green eyes, so vivid and dangerous it glowed behind the glasses met his darkening ones.

The man's eyes narrowed. Emerald gems flashing dangerously down at the unwilling frozen Demon king.

"Who are you?"

What kind of sick powerplay is this?

The numbness in his mouth receded. So the man can control it and still Sucking a harsh breath to reign his rising temper, Muzan glared. 

"I should be the one asking you" Voice low, Muzan conveyed his displeasure and hoped that even with his frozen features, this filth will get the gist of what he’ll do once he got out his restraint. Killing intent flooded the room, filling every nook and corner that even made Akaza shuddered in his place.

The man only raised a skeptical eyebrow, unaffected.

“Who I am isn’t important for burglars like you” titling his to the side in mockery, green eyes roamed up and down. Muzan felt himself bristled at the insult. “Your clothing seems to say otherwise, but your little friend there tried to kill me on the spot and that just means you guys are bad news”

“So, tell me, Who are you” The foolish man asked once again and the air around them constricted with each word that left his lips. The blade stirred in its place in warning. Only the knowledge that it’s not a nichirin blade stopped Muzan from exploding into thousands of pieces. maybe this foolish man hasn’t realized he’s a demon

“And what are you doing in my house?”

.

.

As soon as those words finally registered in his brains, He could only utter one word.

.

.

“What” Muzan deadpanned.


End file.
